This invention relates to hybrid power systems and methods. More particularly, it concerns a hybrid power system and method by which kinetic energy of an inertial load during deceleration is stored and used in a manner to reduce the duration of engine operation for a given period of system operation.
As a result of current emphasis on fuel conservation, it is a well publicized fact that the fuel consumption of an automobile under city driving conditions is considerably higher than under highway driving conditions. The reasons for this are well known and primarily the result of energy losses in decelerating and stopping a vehicle in city traffic, idling operation of the engine while the vehicle is stopped and operation for large percentages of the distance travelled at engine speeds which are above speeds at which engine efficiency is optimum.
Hybrid power systems are known by which the fuel consumption of an automotive engine, particularly under city driving conditions, can be reduced substantially by storing in a flywheel, for example, the kinetic energy of vehicular momentum or negative power made available during deceleration and using the stored energy as an ancillary source of power, as needed, to reduce power demands on the engine or prime mover. Such systems also enable excess power developed by the engine, when operated at improved efficiencies, to be diverted to the flywheel for subsequent use. Moreover, the fuel consuming engine of the system may be shut off when the vehicle is stopped and the flywheel stored energy used both to accelerate the vehicle initially from a stop and to restart the engine.
Substantial reductions in fuel consumption and emission of air pollutants under city driving conditions can be realized with a hybrid system using a relatively simple flywheel represented, for example, by a carbon steel disc a few centimeters in thickness and between 40 and 50 centimeters in diameter rotated at top speeds on the order of maximum engine speeds. A flywheel of this class provides a kinetic energy storage capacity adequate not only to propel a conventional automotive vehicle for limited periods of time but perhaps more importantly, to supply power needed for continued operation of such accessories as power brakes, power steering, air conditioning and the like while the fuel consuming prime mover of the hybrid system is shut off.
In hybrid power systems, some form of infinitely variable or I.V. transmission is usually employed to relate the rotational speeds of the flywheel, the prime mover and the load represented by an automotive drive shaft, for example. While the I.V. transmission has in the past represented a weak link in hybrid power systems, such transmissions have been developed to a state where power in excess of that developed in automotive engines can be transmitted at high efficiencies through infinitely variable output/input speed ratios in a wide range extending to zero. Such transmissions are exemplified by the disclosure of a commonly owned, U.S. Pat. No. 4,152,946, issued May 8, 1979, to Yves Jean Kemper. The state-of-the-art relating to infinitely variable or I.V. transmissions, therefore, provides an existing capability for completely viable hybrid power systems by which the well known energy conserving features of such systems may be realized.
To accommodate highway driving conditions, the power train of an automotive vehicle should be adaptable to a direct driving connection of the prime mover or engine and the load or drive wheel. In prior hybrid systems, highway driving conditions have been met by de-clutching the energy storing flywheel from the drive train (see, for example, Scott, David. "Flywheel Transmission Has Variable-Speed Gear" Automotive Engineering, Mar. 1977, 85:3, pages 18-19 and U.S. Pat. No. 3,672,244-A. L. Nasvytas) or by shunting entirely the flywheel and I.V. transmission components of the hybrid system for transmission of power directly to load (e.g. U.S. Pat. No. 3,870,116-J. Seliber).
While the energy saving potential and operating requirements of hybrid power systems have been recognized in the prior art, therefore, the power train requirements of hybrid systems heretofore proposed have been complex in terms of required controls and component organization, space consuming by comparison to conventional automotive power trains and potentially an additional source of mechanical failure over and above that which already exists in a conventional power train. It is believed that the combination of these several factors, among others, have been a primary deterrent to the use of hybrid power systems in practice.